Method check

src/test/java/org/mapdb/jsr166Tests/TreeMapTest.java:965–1071

min and max are both inclusive. If max < min, interval is empty.

(NavigableMap<Integer, Integer> map,
                      final int min, final int max, final boolean ascending)

     * min and max are both inclusive.  If max < min, interval is empty.
     */
    void check(NavigableMap<Integer, Integer> map,
                      final int min, final int max, final boolean ascending) {
        class ReferenceSet {
            int lower(int key) {
                return ascending ? lowerAscending(key) : higherAscending(key);
            }
            int floor(int key) {
                return ascending ? floorAscending(key) : ceilingAscending(key);
            }
            int ceiling(int key) {
                return ascending ? ceilingAscending(key) : floorAscending(key);
            }
            int higher(int key) {
                return ascending ? higherAscending(key) : lowerAscending(key);
            }
            int first() {
                return ascending ? firstAscending() : lastAscending();
            }
            int last() {
                return ascending ? lastAscending() : firstAscending();
            }
            int lowerAscending(int key) {
                return floorAscending(key - 1);
            }
            int floorAscending(int key) {
                if (key < min)
                    return -1;
                else if (key > max)
                    key = max;

                // BitSet should support this! Test would run much faster
                while (key >= min) {
                    if (bs.get(key))
                        return key;
                    key--;
                }
                return -1;
            }
            int ceilingAscending(int key) {
                if (key < min)
                    key = min;
                else if (key > max)
                    return -1;
                int result = bs.nextSetBit(key);
                return result > max ? -1 : result;
            }
            int higherAscending(int key) {
                return ceilingAscending(key + 1);
            }
            private int firstAscending() {
                int result = ceilingAscending(min);
                return result > max ? -1 : result;
            }
            private int lastAscending() {
                int result = floorAscending(max);
                return result < min ? -1 : result;
            }
        }